Magnetic core for high frequency inductances



Nov. 3, 1936. w. J. POLYDOROFF 2,059,393

MAGNETIC CORE FOR HIGH FREQUENCY INDUCTANCES Filed Dec. 10, 1934 INVENTOR. WLA D/M/e J POL mono/=5 ATTO NEY.

Patented Nov. 3, 1936 UNITED STATES MAGNETIC cons FOR HIGH FREQUENCY mnuc'rancns Wladimlr J. Polydorofl, Chicago, Ill., assignor to Johnson Laboratories, Inc., Chicago, 111., a corporation of Illinois Application December 10, 1934, Serial No. 756,790 In Great Britain December 19, 1938 I i Claims. (01. 171-419) t This invention relates to magnetic cores, and more particularly to magnetic cores suitable for use in high frequency inductances. Magnetic cores of this type may be employed, for example, in inductances intended for use in broadcast receivers. The magnetic cores of the present invention are composed of a finely divided magnetic material, the particles of which are insulated from one another and held together by means of a suitable binder.

The invention will be better understood by reference to the accompanying drawing taken in connection with the description to follow.

Figure 1 shows a core and yoke employed in conjunction with a coil which is tuned by external means;

Figures 2 and 2a show a core with a yoke especially adapted for use with an oscillatorcoil where a constant output frequency is desired.

In my United States Patents No. 1,940,228, issued December 19, 1933, and No. 1,982,689, issued December 4, 1934, and in my co-pending United States application No. 535,606, filed May 7, 1931, there are described magnetic cores of the type hereinbefore referred to.

My present invention results from the discovery that the iron losses occurring in an iron core inductance at high frequencies are chiefly due to the minute induced currents generated in particles in close proximity to the coil, and particu-' vlarly those which lie inside the coil. Likewise the apparent permeability is mostly due to the iron embraced by the coil. It is therefore important to use very finely divided iron of high magnetic properties in the central plug of such a core. The magnetic structure employed to provide a return path for the flux, on the other hand, is subjected to a much lower influence tending to create induced currents and is therefore less important from the standpoint of losses. ,Thus for instance the outer yoke can be made of coarser and inferior magnetic material without having a serious adverse effect upon the performance of the inductance device as a whole.

The present invention may be advantageously employed in inductances having fixed cores, such as for instance, inductances tuned by external means. For example, a. magnetic core for a high frequency inductance may have associated with it a U-shaped yoke to reduce the reluctance of the magnetic flux path and thus to increase the.

apparent permeability of the core. The yoke in this case also may be made of magnetic material coarser than and inferior to that employed in the core, or in particular cases it may even consist of laminations or sheet magnetic material,

thereby greatly reducing the reluctance of the return path. By locating the yoke sumciently far from the direct influence of the coil. the core losses may be kept sufficiently low despite the lower grade of material employed in the yoke.

In Figure 1, a compressed commlnuted netic core 6 supports coils I, which may of pancake form as shown, and which are connected in series in order to exhibit low loss characteristics. The magnetic yoke 8, may also be 01 compressed commlnuted magnetic material of an inferior grade to that employed in the core 9.

The construction shown inFigures 2 and 3a ll of particular value for use in conjunction with the oscillator coil of a superheterodyne receiver. It is well known that such oscillators are subject to frequency drift due to changes in temperature and in the voltage supplied to the oscillator valve. One method for limiting frequency drift due to temperature changes consists in employing a coil provided with a core made of a material having properties such that its apparent permeability also changes with temperature; a material having such properties is, for instance described in my United States Patent No. 1,982,689. Such a core, for example, may be employed in the construction shown in Fig. 1.

It was found that commlnuted materials such as disclosed in my United States Patent No. 1,982,689, retain their permeabilities constant through a considerable range of magnetic intensities and are in practice operated far below their saturation points.

According to the present invention it was found useful to employ in certain cases magnetic material whose magnetic properties could be varied, and to provide magnetizing windings by means of which their magnetic properties can be controlled. In the particular case of an oscillator-generator where the losses are of no great importance the return path of the inductance coil (Figure 2) may be of thinly laminated iron employing for instance, silicon iron strips, whereas the core piece 6 surrounded by the windings I is made of usual commlnuted material. The yoke 8 of this structure is such that its effect on the cpre piece 8 may be varied by external fields represented by a coil 12 which may be suppliedwith direct current from either the power supply or the anode circuit of the oscillator valve, or both. i 1

Thus the degree of D. C'. magnetization and hence the effective permeability of the core structure and the total inductance of the coil may be made to vary automatically with changes in the power supply or anode voltages. This arrangement effectively limits frequency drifts and maintains the oscillator circuit substantially constant with frequency notwithstanding small variations in the power supply voltage.

Figure 2 shows an elevation of an inductance device arranged for compensation of frequency drifts by D. C. magnetization effect. Figure 2a is a plan view of the same device. A cylindrical magnetic core 6 supports pancake inductance coils I. The yoke 8 is made of thin laminations of magnetic material, and carries a direct-current winding l2.

It will be understood that the core 6 of this embodiment may be so chosen that its permeability varies in response to temperature variations in a suitable manner as hereinbefore described so that both voltage supply and temperature variations may be compensated for in one instrument.

Having thus described my invention, what I claim is:

"1. A frequency-controlling device for use with a generator of high-frequency currents, said generator being subject to frequency fluctuations with changes in operating conditions, including an inductor having a compressed comminuted ferromagnetic core and a low-loss coil for said highirequency currents, and means for regulating the inductance of said inductor including a magnetic structure which completes the magnetic circuit of said inductor, said structure being made of material whose magnetic reluctance is varied in response to changes in operating conditions, in such manner as to maintain the frequency of the current delivered by said generator substantially constant.

2. A frequency-controlling device for use with a generator of high-frequency currents energized from an external power source that is subject to voltage variations which tend to produce fluctuations in the frequency of the current delivered by said generator, including an inductor having a compressed comminuted i'erro-magnetic core and a low-loss coil for said high-frequency current, and means for regulating the inductance of said inductor including a magnetic structure which completes the magnetic circuit of said inductor, said structure being made of laminated material whose reluctance may be varied in response to changes in magnetizing current, and a winding for said magnetizing current so connected to said external source of power as to maintain the frequency of the current delivered by said generator substantially constant.

3. A frequency-controlling device for use with a generator of high-frequency currents energized from an external source of power that is subject to voltage variations which tend to produce fluctuations in the frequency of the current delivered by said generator, said generator being also sub- Ject to frequency fluctuations with changes in temperature, comprising an inductor having a compressed comminuted form-magnetic core made of material whose magnetic reluctance varies in response to temperature, a magnetic structure which completes the magnetic circuit of said inductor made of laminated material whose reluctance may be varied in response to changes in magnetizing current, and a winding for said magnetizing current connected to said external source, whereby voltage variations and temperature changes produce compensating variations in the reluctance of the magnetic circuit so as to maintain the frequency of the current delivered by said generator substantially constant.

WLADIMIR J. POLYDOROFF. 

